The present invention relates to a modem for transmitting digitally coded information between an information distribution network such as a telephone network, and either a central data processing unit or a remote data processing unit. More particularly, the invention relates to a modem whose operation is controllable by one of the very same data processing units for which it is designed to establish a communication link.
Modems are widely used to establish communication links between information distribution networks, e.g., telephone distribution networks, and data processing units. In general, modems modulate when transmitting and demodulate when receiving, signals usable by data processing units so that the information represented by such signals is in a form transmittable over a selected distribution network.
Present day modems provide quite reliable transmission of digitally coded information over telephone distribution networks. However, their control leaves much to be desired. Although modems provide data transmission at the quite high feed rates which can be accommodated by many data processing units, most provide few, relatively cumbersome, control options. For example, stand-alone modems, i.e., modems for use with data processing units which themselves do not have modems built in, require control separate and apart from the data processing units. Because of such, the control functions which have been made available for stand-alone modems have been quite limited. The most "sophisticated" stand-alone modem control known to applicant at the time of filing this application, merely provides automatic dialing. That is, such modem is capable of establishing a communications link over a distribution network without an operator having to actually dial the desired number on a telephone.
The control functions of even those modems which are provided as a part of a data terminal, i.e., are directly incorporated into the data terminal, leave much to be desired insofar as their control is concerned. The approach in the past has been to provide separate keys which are directly connected with the various integrated circuit chips providing modem operation. This also results in the control functions for such modems being generally quite limited.